The present invention relates to blood vessel clamps.
Blood vessel clamps are used in surgical procedures to reduce or cut off the blood flow or supply in veins or arteries.
Such clamps, known for example from EP-A-218544, conventionally consist of scissor-like structures having mating gripping jaws instead of cutting blades. In addition a ratchet mechanism is provided on each arm. The two ratchet mechanisms engage during the last stages of approach between the two jaws so as to prevent the jaws from moving apart. Each ratchet mechanism is in the form of a projection extending from one arm of the clamp at a position adjacent the finger hole, towards the other arm of the clamp. The leading edge of each arm is so profiled that when the two edges engage they are displaced away from one another in a direction normal to the direction of motion so that the lower surface of one projection can then ride over the upper surface of the other projection, as the two projections continue to move towards one another. The two facing surfaces of the projections are each provided with a saw-tooth profile. The saw teeth interlock with one another and prevent the two projections moving away from one another but allow continued movement towards one another to increase the number of the teeth of the two portions interlocking with one another. Thus a series of spaced discrete locking positions is achieved as the two jaws move together. To release the teeth from one another, the two projections must be first moved towards one another to a position intermediate the adjacent locking positions and then displaced in perpendicular direction to cause the two sets of teeth to disengage one another before the arms of the clamp can be moved apart.
Such clamps have serious disadvantages. In use when a blood vessel is held between the jaws, the blood flow is monitored as the jaws are closed. When the blood flow reaches the desired level or stops, the jaws usually need to be closed further to reach the nearest locking position. Furthermore, to unlock the jaws, the jaws have to be closed tighter still before the ratchet mechanisms can be disengaged. This results in a greater pressure being applied to the vessel than is necessary and this can lead to damage of the vessels particularly if there has been a build up inside the vessel of calcium or other material. Still further, the crushing or fragmentation of such a build up may mean that the fragments are subsequently released into the blood supply system with the consequent danger of a thrombosis or blockage in another part of the system.